U.S. patent number 5,642,713 [Application Number 08/525,784] was granted by the patent office on 1997-07-01 for process for controlling a piston internal combustion engine by maintaining the running limit.
This patent grant is currently assigned to FEV Motorentechnik GmbH & Co. Kommanditgesellschaft. Invention is credited to Heinrich Mayer, Guenter Schmitz.
United States Patent |
5,642,713 |
Schmitz , et al. |
July 1, 1997 |
Process for controlling a piston internal combustion engine by
maintaining the running limit
Abstract
A process for controlling a piston internal combustion engine by
maintaining a running limit thereof. The process includes the steps
of: detecting in at least one cylinder, over at least one work
cycle and without reference to a crankshaft position of the engine,
a measured variable which is influenced by a conversion of fuel
into energy; setting the measured variable in relation to a
detected, stored measured variable of at least one previously
intercepted work cycle; and producing an adjusting signal from any
deviation between the measured variables for inputting the
adjusting signal to an engine regulation system. The measured
variable can be either a pressure course, a light intensity or an
ion current corresponding to the combustion process within the
engine.
Inventors: |
Schmitz; Guenter (Aachen,
DE), Mayer; Heinrich (Aachen, DE) |
Assignee: |
FEV Motorentechnik GmbH & Co.
Kommanditgesellschaft (Aachen, DE)
|
Family
ID: |
6509150 |
Appl.
No.: |
08/525,784 |
Filed: |
October 4, 1995 |
PCT
Filed: |
January 31, 1995 |
PCT No.: |
PCT/EP95/00338 |
371
Date: |
October 04, 1995 |
102(e)
Date: |
October 04, 1995 |
PCT
Pub. No.: |
WO95/21322 |
PCT
Pub. Date: |
August 10, 1995 |
Foreign Application Priority Data
|
|
|
|
|
Feb 1, 1994 [DE] |
|
|
44 02 938.1 |
|
Current U.S.
Class: |
123/435 |
Current CPC
Class: |
F02D
41/0052 (20130101); F02D 41/1498 (20130101); F02D
35/02 (20130101); Y02T 10/47 (20130101); F02D
35/021 (20130101); Y02T 10/40 (20130101); F02D
35/022 (20130101); F02D 35/023 (20130101) |
Current International
Class: |
F02D
35/02 (20060101); F02D 41/00 (20060101); F02D
41/14 (20060101); F02D 041/04 (); F02D
043/00 () |
Field of
Search: |
;123/425,435
;73/35.03,35.04,35.08,35.12 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 297 951 |
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Jan 1989 |
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EP |
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0 370 594 |
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May 1990 |
|
EP |
|
0 579 271 |
|
Jan 1994 |
|
EP |
|
29 06 782 |
|
Sep 1980 |
|
DE |
|
33 15 048 |
|
Oct 1983 |
|
DE |
|
33 14 225 |
|
Oct 1984 |
|
DE |
|
WO89/11031 |
|
Nov 1989 |
|
WO |
|
Other References
Patent Abstracts of Japan, vol. 5, No. 90 (M-73) 12 Jun. 1991 &
JP, A, 56 038 559 (Daihatsu Motor Co.). .
IEE Proceedings D. Control Theory & Applications, Bd. 136, Nr.
2, Mar. 1989, Stevenage GB Seiten 84-88, "Engine Control System
Using A Cylinder Pressure, Sensor", Y. Hata et al..
|
Primary Examiner: Wolfe; Willis R.
Attorney, Agent or Firm: Spencer & Frank
Claims
We claim:
1. A process for controlling a piston internal combustion engine by
maintaining a running limit thereof comprising the steps of:
detecting in at least one cylinder, over at least one work cycle
and without reference to a crankshaft position of the engine, a
measured variable which is influenced by a conversion of fuel into
energy;
setting the measured variable in relation to a detected, stored
measured variable of at least one previously intercepted work
cycle; and
producing an adjusting signal from any deviation between the
measured variable and the stored measured variable of the at least
one previously intercepted work cycle for inputting the adjusting
signal to an engine regulation system.
2. The process according to claim 1, wherein the measured variable
is a pressure course of a corresponding combustion process within
the engine and the stored measured variable is a stored pressure
course of a corresponding combustion process within the engine.
3. The process according to claim 1, wherein the measured variable
is a light intensity of a corresponding combustion process within
the engine and the stored measured variable is a stored light
intensity of a corresponding combustion process within the
engine.
4. The process according to claim 1, wherein the measured variable
is an ionic current of a corresponding combustion process within
the engine and the stored measured variable is a stored ionic
current of a corresponding combustion process within the
engine.
5. The process according to claim 1, wherein detected measured
variables corresponding to respective work cycles are set in
relation to one another by comparison.
6. The process according to claim 5, wherein the detected measured
variables are set in relation by subtraction.
7. The process according to claim 5, wherein the detected measured
variables are set in relation by statistical evaluation.
8. The process according to claim 1, wherein a cross-correlation
function of a detected, influenceable measured variable is formed
with a similar time-delayed influenceable measured variable and
characteristics are derived from the cross-correlation function
which are to be set in relation to one another.
9. The process according to claim 8, wherein a respective maximum
of the cross-correlation function constitutes a characteristic.
10. The process according to claim 8, wherein a change in a
detectable measured variable, in particular of pressure course as a
function of time, is detected as an evaluation characteristic for a
setting in relation.
11. The process according to claim 10, wherein a time interval
within which a passage through a predetermined threshold value for
the detected, influenceable measured variable, in particular of
combustion chamber pressure between pressure increase and pressure
decrease, occurs is detected as a comparison characteristic.
12. The process according to claim 11, wherein a pulse to
no-current ratio between successive passages through the threshold
value comprising a chronological succession of square-wave pulses
is detected as a comparison and evaluation characteristic.
13. The process according to claim 12, wherein an evaluation is
performed by forming a standard deviation via a detection of a
succession of a predetermined number of work cycles, preferably
10.
14. The process according to claim 13, wherein the standard
deviation is standardized by forming a mean value.
15. The process according to claim 14, wherein to form at least one
of the standard deviation and the mean value, one of a constant
number of work cycles and a constant duration is specified in each
case.
16. The process according to claim 11, wherein upon detection of
the pressure course as the influenceable measured variable, the
threshold value is changed as a function of at least one of
detected maximal pressure and a mean effective pressure derived
from the detected maximal pressure of one of a work cycle and a
succession of work cycles.
17. A device for performing the process according to claim 11,
wherein the threshold value is plotted by regulation to a constant
duty factor.
18. The device for performing the process according to claim 17, in
a reciprocating piston internal combustion engine, in which at
least one cylinder is connected to a sensor for detecting a
measured variable which can be influenced by a conversion of fuel
into energy as a function of time, which sensor is connected to a
characteristic former for forming a characteristic signal which is
derived from the influenceable measured variable, a signal output
of the characteristic former being connected to an evaluation
unit.
19. The device according to claim 18, wherein the characteristic
former has a comparator and an integrator for mean value formation
whose signal input is respectively connected to the sensor, and in
which a signal output of the integrator is connected to the
comparator, and wherein a characteristic signal to be supplied to
the evaluation unit is present at a signal output of the
comparator, preferably as a square-wave signal.
20. The device according to claim 19, wherein the signal output of
the comparator is connected to an integrator and to an edge
detector for producing a pulse to no-current ratio from the
characteristic signal, and wherein the signal output of the
integrator is connected to a sample-and-hold circuit, while a
signal output of the edge detector is connected to the integrator
and to the sample-and-hold circuit, a signal output of the
sample-and-hold circuit being connected to a signal output.
21. The device according to claim 20, wherein the signal output of
the sample-and-hold circuit has a mean value former and a
subtractor which are connected to a signal output of the evaluation
unit and wherein a signal output of the subtractor is connected to
an absolute value former which sends an adjusting signal.
22. The device according to claim 21, wherein an integrator,
preferably a transient integrator for the adjusting signal, is
connected to an output side of the absolute value former.
23. The device according to claim 18, wherein a signal output of
engine electronics for controlling engine operation is connected.
Description
FIELD OF THE INVENTION
The invention pertains to a process for controlling a piston
internal combustion engine.
BACKGROUND OF THE INVENTION
The constantly increasing demands for pollution reduction have
recently led to the introduction of concepts involving a lean fuel
mixture and concepts involving exhaust recirculation, among others.
Lean fuel mixture concepts have the advantage of making fuel
economy is possible, in addition to leading to a reduction of raw
emissions. With exhaust recirculation concepts, when a 3-way
catalytic converter is used at the same time, a particularly good
reduction of overall emissions is possible.
It is common to both concepts that in certain operating ranges of
the engine, it is desirable to use a fuel which is leaned down as
much as possible and to establish a high exhaust recirculation
rate, respectively, while necessarily maintaining a certain margin
from the so-called "running limit." The "running limit" can be
defined as the limit of the leaning down and/or or of the exhaust
recirculation rate beyond which ignition of the mixture no longer
occurs reliably for every piston working cycle, where an acceptable
running smoothness of the engine does not occur, or where exhaust
emissions begin increasing again because of insufficient
combustion. Because of the need to maintain a required margin from
this running limit, the potential of these two concepts, that is,
the potential of using lean fuel mixtures and of recirculating the
exhaust, is not completely utilized.
Principles for recognizing the running smoothness of the engine are
disclosed in DE-A-29 06 782 for lean regulation by using a
rotational irregularity sensor, in DE-A-33 15 048 by means of
structure-borne sound sensors, and in DE-A-33 14 225 via an exhaust
volume flow measurement, as well as in other prior publications.
Recognizing the "running limit" by making use of rotational
irregularity can be used principally in engines that are on the
test bench. However, the above cannot be accomplished in the case
of engines disposed in production vehicles, since uneven spots in
the road, which lead to misleading signals, are fed in via the
drive train.
In practice, the recognition of the "running limit" in a production
vehicle via structure-borne sound sensors is hardly usable either.
Besides possible input resulting from uneven spots in the road,
there are also a wealth of interfering signals, which lead to
problems of misinterpretation because of an extremely poor
signal-noise ratio, which is due to the relatively low useful
signal that can be detected.
Additionally, an analysis of the exhaust volume flow is relatively
complicated to perform and, consequently, cannot be introduced in
production vehicles at least for cost reasons.
The use of combustion chamber pressure sensors for recognizing the
running limit has previously been intensively employed in the
development of engine tuning. The tuning is performed each time
such that a distinct margin from the lean running limit is
maintained. With the availability of fairly inexpensive but quite
precise combustion chamber pressure sensors, this method has
meanwhile been introduced even in production vehicles, by providing
lean regulation. References to the above are found in publications
SAE 930882 and 930351 of the 1993 SAE Congress in Detroit. In the
process proposed in the above publications, an estimate of the
effective torque is derived from the combustion chamber pressure.
In addition, the pressure values of certain positions of the
crankshaft are estimated and from the same, an estimate of the
internal work performed by the engine is derived. The above process
relies on the process for tuning engines which is practiced on the
test bench, and in which the so-called indicated mean effective
pressure, i.e. the contour integral of the pressure, is determined
via the cylinder volume. A measure for the running smoothness is
derived via statistical methods from the above internal work or
from the estimated moment introduced. In the above process,
however, knowledge of the crankshaft state is critical to the
derivation of the current volume of the combustion chamber from the
respective structural data of the relevant engine. For the above
reason, in mass production of running limit recognition according
to this method, the signal of the combustion chamber pressure
transducer is supplied to a processing circuit, which receives
information about the state of the crankshaft from a crankshaft
angle marking sensor as a further input signal. The processing
circuit is integrated into the engine control electronics remote
from the sensor, since the crankshaft angle marking transducer
signals are also available at that location. As a result, however,
each manufacturer encounters the necessity of specifically
implementing an algorithm in the engine electronics that perform
the corresponding evaluation. If this recognition is realized with
software in an already existing processor of the engine control
electronics, then this software function can be integrated into
existing engine control software only at a high cost. In order to
avoid the above, a second processor must be employed, which,
however, require a redesign of all the electronic hardware of the
engine.
SUMMARY OF THE INVENTION
The object of the invention is to now to achieve a process for
recognizing the running limit which allows the running limit to be
regulated, thus preventing the running limit from being exceeded,
as could happen for example as a result of changing ambient
conditions, at such favorable cost that this regulation can be used
in production vehicles.
The above object is attained according to the invention by
maintaining a running limit thereof. The process includes the steps
of: detecting in at least one cylinder, over at least one work
cycle and without reference to a crankshaft position of the engine,
a measured variable which is influenced by a conversion of fuel
into energy; setting the measured variable in relation to a
detected, stored measured variable of at least one previously
intercepted work cycle; and producing an adjusting signal from any
deviation between the measured variables for inputting the
adjusting signal to an engine regulation system. The measured
variable can be either a pressure course, a light intensity or an
ion current corresponding to the combustion process within the
engine. The above process forgoes the detection of the crankshaft
position and uses only the detected, influenceable measured
variable to determine the running limit. For the measured variable
which can be influenced by the conversion of fuel into energy
and/or exhaust (for example pressure course per work cycle, light
intensity of the combustion process per work cycle, ionic current
measurement per work cycle), sensors are already available. Hence,
through these sensors, a signal is already available that directly
represents the current status of conversion of the fuel into energy
and/or exhaust in the cylinder and enables the detection and
formation of a signal derived from the signal without additionally
having to have recourse to a crankshaft angle marking transducer or
having to tap into existing systems. By comparing the influenceable
measured variable, which is detected in one or more previously
intercepted work cycles, with the deviations resulting from the
same, a conclusion is drawn as to whether the predetermined running
limit and hence the desired running smoothness of the engine is
being maintained by the status of regulation at the time of the
comparison. Therefore, without loss of running smoothness, the
engine regulation can be brought much closer to the running limit
without exceeding the same. It is especially advantageous in this
case that not all of the cylinders of an engine have to be
monitored; it is sufficient to detect the influenceable measured
variable in one cylinder. In this connection, it is advantageous
if, in a given engine, the cylinder which will reach the running
limit the soonest, as can be the case for example if there exists a
structurally dictated uneven distribution in the intake tube, is
chosen. However, if all cylinders should behave practically
identically with regard to the running limit, then by purposeful
"mistuning" of the system it can be assured that a predetermined
cylinder is always the first to reach the running limit. In the
event of lean regulation, this can be done by consistently
injecting a smaller quantity into one cylinder than into the other
cylinders. Since in operation this cylinder is now the first to
reach the running limit, one can be certain that if running limit
regulation is done with respect to this cylinder, all the other
cylinders will still have sufficient running smoothness;
consequently the overall running smoothness and the overall
emissions values are reliably kept within the required limits.
In a preferred embodiment of the process according to the
invention, it is provided that the measured variable which can be
influenced by fuel conversion corresponds to the course of pressure
in the work cycle. For the sake of measuring the running smoothness
or of determining the running limit without using a crankshaft
angle marking transducer signal, it is in fact particularly
suitable for the course of pressure in the combustion chamber,
because it is so conclusive and because of its favorable
signal-noise ratio, to be detected as the measured variable that
can be influenced by means of the conversion of fuel.
In another embodiment of the process according to the invention, it
is provided that the measured variable, which can be influenced by
the fuel conversion into energy and/or exhaust corresponds to the
light intensity of the combustion process. The point at which
combustion begins and at which it ends can be recognized
particularly well by registering the light intensity at each work
cycle. The light intensity may then be compared to signals of
previously intercepted work cycles previously detected at intervals
and from the above comparison a corresponding adjusting signal can
be derived.
In another embodiment of the process according to the invention, it
is provided that the measured variable which can be influenced by
the fuel conversion into energy and/or exhaust is measured by means
of an ionic current, which changes during the combustion
process.
Advantageous embodiments and improvements of the process according
to the invention, in particular with regard to the evaluation of
the detected, influenceable measured variable will be described
further below.
To realize the process according to the invention, the invention
further provides a device for performing the process in a piston
internal combustion engine, in which at least one cylinder is
connected to a sensor for detecting a measured variable
corresponding to the conversion of fuel into energy, as a function
of time; this sensor is connected to a characteristic forming
device for forming a characteristic signal, which is derived from
the detected measured variable, and the signal output of the
characteristic forming device is connected to an evaluation unit.
The advantage of the above device is comprised in concerns the
possibility of connecting the device to an already existing
electronic engine control system without changing the software and
hardware.
Further advantageous embodiments of the device according to the
invention are explained as set forth below.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is illustrated by way of example in the drawings.
FIG. 1 is a graph of the running smoothness and the emissions
versus the air ratio lambda;
FIG. 2 is a block circuit diagram of the process according to the
invention;
FIG. 3 is a graph of pressure courses versus crankshaft angle in an
overlay;
FIG. 3a is a graph of two different pressure courses versus
crankshaft angle in chronological succession;
FIG. 4 is a schematic representation of an evaluation circuit;
FIG. 5 is a graph showing the course of the output signal of the
circuit according to FIG. 4 for different operational states;
FIG. 6 is a schematic black circuit representation of the circuit
according to the invention connected with an internal combustion
engine;
FIG. 7 is a graph of light signals used as measured variables
corresponding to the fuel conversion;
FIG. 8 is a schematic representation of an ionic current device for
measuring the measured variable corresponding to the fuel
conversion;
FIG. 9 is a graph of the course of the ionic current versus time
during a work cycle;
FIG. 10 is a graph of the course of cylinder pressure versus time
during a work cycle similar to the one according to FIG. 9.
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 1, the course of the emissions (curve 1) and the changing
of running smoothness (curve 2) are shown as a function of the air
ratio number lambda. As can be seen from curve 1, with increasing
leaning of the fuel mixture, or with increasing exhaust
recirculation, and the attendant increase in the air ratio number,
the emissions shown in curve 1 drop to a minimum. After a minimum
is achieved, the emissions rise sharply.
In comparison with the above, the running smoothness represented by
curve 2 remains constant over wide ranges, until it rises in the
region of the emissions minimum. In this way, the so-called running
limit 3 is established as the limit for the exhaust recirculation
rate or the leaning beyond which the ignition of the mixture no
longer occurs in every engine work cycle as reliably, causing the
measure of acceptable running roughness to be exceeded. The running
limit 3 consequently divides region A of "running smoothness" from
region B of "running roughness".
The process is explained in relation of the block circuit diagram
according to FIG. 2. A sensor 4, via which a measured variable
(pressure, light, ionic current) which can be influenced by i.e.,
which corresponds to the conversion of fuel into energy and/or
exhaust is detected as a function of time, furnishes a course
signal to a device for forming characteristics, or to a forming
device 5. At least one characteristic is extracted from the course
signal, and in a subsequent processing stage 6, this characteristic
is "set in relation" to one or more characteristics from the course
signals of previous work cycles or at least of one previous work
cycle. In that regard, this "setting in relation" can be a simple
comparison, a subtraction, or a statistical evaluation. However,
this setting in relation can also be done by forming a
cross-correlation function of the course signal with a similar,
time-delayed signal course. This cross-correlation function yields,
in turn, characteristics that can be compared to one another. A
particularly highly suitable characteristic is the respective
maximum of the cross-correlation function, which represents a
measure for the speed of two successive work cycles. By means of
the comparison, subtraction, or statistical evaluation of precisely
this maximum (generally of extracted characteristics), a conclusion
is now drawn about the statistical fluctuations of the combustion
process, about the measured variable which can be influenced by the
conversion of fuel, and consequently about the running smoothness
or running roughness of the engine.
In FIG. 3, the above is explained in further detail via the
detection of the pressure course as the measured variable which can
be influenced by the conversion of fuel into energy and/or exhaust.
In an overlay in FIG. 3, a plurality of pressure course signals 7,
8, 9, and 10 are depicted as a function of the crankshaft angle.
When the pressure course is selected, the "width" of the pressure
course curve at a predetermined pressure is determined as the
measured variable to be detected. In the exemplary embodiment shown
in FIG. 3, the indicated width a results from the pressure course
curve 7 at the indicated threshold value of 7 bar. Upon a
subsequent measurement under altered operating conditions, such as
increased leaning down, a pressure course curve 8 with a visibly
lower peak pressure is the result. Nevertheless, the "width" of the
pressure course detected here is unchanged, so that the ignition of
the mixture is still performed reliably, and accordingly there is
no change in the running smoothness.
As can be seen from the pressure course curves 9 and 10, if the
pressure is now further reduced as the leaning down is further
intensified, then a clear reduction of the "width" of the pressure
course curve to the measure b or c is the result. The comparison
between pressure course 9 and pressure course 10 shows that at
equal maximal pressure, the combustion process is different, and so
from this it can already be concluded that the running smoothness
between these two work cycles already leads to considerable
deviations.
Depending on the characteristic curve of the engine, the system may
be made more sensitive by selecting the threshold values. As can be
seen from FIG. 3, a reduction of the threshold value from 7 to 5
bar already leads to a distinct spreading, and therefore to an
increase in the differences between the relevant "widths" a, b, and
c.
In FIG. 3a, the process described in FIG. 3 is shown in
chronological succession, but in a reverse order, for a threshold
value of 5 bar.
In a preferred embodiment of the invention, the pressure signal
course is first compared to a threshold value and is consequently
available as a square-wave signal at the output of the comparison.
Instead of now evaluating the width of the square pulse, which can
naturally also be done by the proposed process, the measurement of
the pulse to no-current ratio, i.e. the duty factor, of this train
of square pulses is particularly advantageous for further
evaluation. An improvement in lower sensitivity to rapid
engine-speed fluctuations is achieved as a result. The pulse to
no-current ratio can now in turn be compared to the preceding
measurement values for the duty factor according to methods using
chronological comparison, or subtraction, or according to
statistical methods. The method involving chronological setting is
performed in the evaluation stage 6.
The use of the standard deviation has shown itself to be
particularly suited for the evaluation algorithm in the evaluation
stage 6. This standard deviation can be formed over a number of the
last n cycles, for example. The value 10 has proven to be
particularly favorable for n, since it represents an optimal
compromise between reaction speed and lowering sensitivity to
interfering influences. As postprocessing of the standard deviation
in the evaluation stage 6, this standard deviation can be
advantageously standardized to reduce an influence of the
respective load point of the internal combustion engine. For this
standardization, it is especially advantageous to use the mean
value of the signal. The formation of the mean value can be done
either from the extracted characteristic alone ("width" of the
pressure course signal, light measurement, ionic current) or from
the actual mean value of the detected measured variable, for
example of the pressure course signal. The period of time for
forming the mean value can either be coupled to the period of time
for forming the standard deviation or be freely chosen in
accordance with other criteria. The best compromise for the
respective use is likewise determined by doing the above. For
applications involving high dynamics, the period of time is
selected to be relatively short, whereas for stationary motors, for
example, the period of time for forming the mean value can be
selected to be quite long. For practically employed production
engines, a number of about 10 cycles has again been found to be
normally favorable.
To form the standard deviation and the mean value, the measuring
window can involve either a constant number of cycles (pulses) or a
constant duration.
The threshold value described by FIG. 3 has different optimal
settings for different load points. As a result, it is very
practical to allow this threshold value to be determined
automatically. One possible way to determine the threshold value is
to use the value of the preceding pulse to no-current ratio, which
gives an indication as to what the "relative level" is for the
detected measured variable, for example the combustion chamber
pressure, at the threshold value. Another possible way of
determining and plotting the threshold value is to evaluate the
maximum and/or the mean value of the detected measured variable,
for example the pressure. However, the determination of the
threshold value is not limited to the above characteristics. Other
characteristics and methods can also be found that enable automatic
adaptation of the threshold value, for example in the form of a
regulation to a constant duty factor.
The complete running smoothness recognition circuit (comprising the
characteristic former 5 and the evaluation stage 6) and also
individual parts of the evaluation unit can be designed in either
analog or digital form, or as a microprocessor circuit.
FIG. 4 illustrates an exemplary embodiment via which the process,
functioning in accordance with the pulse to no-current ratio, can
be performed in analog form. The measured variable signal 7, which
is detected by the sensor 4, is first supplied to a comparator 8
and compared to the mean value 10, which is formed via the
integrator 9. The above-described square-wave signal 11 is then
available at the output of the comparator 8. In the subsequent
stage, the signal is added up in an integrator 12 to determine the
pulse to no-current ratio. At the beginning of each cycle, the
integrator 12 is reset to "0". At the end of each cycle, the value
of the integrator 12 is transferred to a sample-and-hold circuit
13. Resetting the integrator 12 and the transfer to the
sample-and-hold circuit are controlled via an edge detector 14,
which evaluates the signals coming from the comparator output.
At the output 14 of the sample-and-hold circuit 13, there is now a
value which represents the duty factor of the signal. This signal
is now supplied on the one hand to a mean value former 15, also
called an integrator here, which is responsible for forming the
mean duty factor. This mean value 16 formed is now compared to the
respective incoming signal 14 by means of a subtractor 17. The
output signal present at the subtractor goes through an absolute
value former 18 and can then either be immediately output or goes
through one more transient integration stage 19, which further
carries out a certain smoothing of the output signal.
To clarify the functioning of the overall circuit, let it first be
assumed that the engine runs very smoothly, and hence the measured
variable detected, for example the combustion chamber pressure, is
practically the same in one cycle as it is in each subsequent
cycle. Then a square pulse train with a constant pulse to
no-current ratio is formed at the output of the comparator 8. This
leads to a constant signal at the output of the integrator 12 or
the sample-and-hold circuit 13. This constant signal is averaged on
the one hand in the mean value former (transient integrator 15) and
compared to the respective actual signal 13.1. However, since the
actual signal practically always corresponds to the mean value, a 0
signal is produced at the output of the subtractor 17.
Next, let it be assumed that the engine is brought out of this
operating state into an operating state in which it is operated at
the running limit. Due to the cyclical fluctuation of the measured
variable detected, for example of the pressure course signal, now
the output pulse train of the comparator 8 will have a different
duty factor. As a result, there are constantly changing values at
the output of the sample-and-hold stage 13. If these are now
compared to their own mean value 16, then the result is sometimes a
positive and sometimes a negative difference. All the differences
are converted to positive values by the absolute value for 18,
which is inserted on the output side of the subtractor 17. On the
output side of the transient integrator 19, which follows the
absolute value former, a signal is now available, which becomes
larger as combustion chamber pressure courses behave more
irregularly. Consequently, this signal represents a measure of the
running smoothness or the running roughness of the engine.
The depiction described in FIG. 5 shows an output signal of a
digitally designed evaluation circuit as a standard deviation from
the duty factor of each ten successive cycles of the engine. In
this connection, curve course 20.1 shows the latter-described case
of major running roughness, while curve course 20.2 shows a mean
operating state with running roughness, and curve course 20.3 shows
an operating state with slight running roughness, i.e. good running
smoothness. The strong dependence of the signal on the running
roughness of the engine can be clearly recognized. It can also be
seen that even at a principally constant operating point of the
engine, a transient alteration of the running smoothness leads to
an output signal which changes acutely (and considerably), as can
be seen in signal curve 20.1. Within about twenty work cycles, the
regulation is plotted in such a way that low running roughness,
i.e. pronounced running smoothness, is achieved.
FIG. 6 shows a means of running smoothness regulation in the form
of a block circuit diagram. A sensor 22 with an integrated running
smoothness recognition circuit of the above described type is
connected to an engine 21 equipped with exhaust recirculation. The
running roughness signal 20, which comes from the running
smoothness recognition circuit of the sensor 22, is sent to the
engine electronics 23, where it is supplied for example to a PID
controller 24.
First, a certain exhaust recirculation value is given to the
exhaust recirculation valve 25 by means of a precontroller that
operates in the manner of a performance graph. If the running limit
is now reached, the PID controller assures that the exhaust
recycling signal is changed until the desired value for the running
smoothness has been established (see curve course 20.2 in FIG.
5).
In lieu of the above described process of evaluating the pressure
course as a measured variable which can be influenced by the
conversion of fuel into energy and/or exhaust, it is also possible
by the process to evaluate light signals which are obtained from
the combustion chamber. To do so, optical access to the combustion
chamber is created; this can be done for example in the form of a
modified spark plug. The light signal is first converted into an
electrical signal via a corresponding sensor, for example a
photodiode, a phototransistor, a photomultiplier, or the like. The
resultant electrical signal is described in FIG. 7 by diagram 26,
which is shown here simultaneously with diagram 27 of the
affiliated pressure course of the combustion chamber pressure. The
point at which the combustion begins and the point at which the
combustion ends in the observed part of the combustion chamber can
be recognized particularly well from the light signal.
The measurement signal, which is obtained thus from the measured
variable "light" can now be evaluated according to the desired
characteristics, as is described in FIGS. 4 and 6. In diagram 26,
the signal width "b" for example is shown for a predetermined light
intensity threshold. The further processing is then performed as
described by FIG. 4 for the "width" of the pressure signal. As with
the processing of the pressure signal, in processing the light
signal, one is also not limited to the evaluation of the "width" or
of the duty factor; instead, other characteristics of the light
signal can also undergo the subsequent statistical evaluation.
FIG. 8 shows the application of the process to the evaluation of
the ionic current as a further possibility for detection of a
measured variable which is influenced by the conversion of fuel
into energy and/or exhaust. Two measurement electrodes 29 (or one
measurement electrode, in a unipolar embodiment), which are
connected to a constant voltage source 30, are disposed in the
combustion chamber 28 of a cylinder of a reciprocating piston
internal combustion engine. Normally, no current flow occurs now
between the two measurement electrodes 29, provided that small
leakage currents are disregarded. In the course of the work cycle,
if the electrodes 29 are now engaged by the flame front 31 which is
schematically represented here, then there is an ionizable gas in
the region of the electrodes 29, and so an ionic current flows
between the two poles of the measurement electrodes 29. This ionic
current can now be measured. In lieu of measuring the ionic
current, the change in the d.c. voltage applied can also be
measured, which is produced at the electrodes at the start of the
ionic current flow.
A d.c. voltage supply that operates in a voltage range between 50
and 100 volts has proven to have a particularly well-suited voltage
range. In principle, the process also functions at other
voltages.
FIG. 9 schematically shows the ionic current or probe voltage that
is established over time. Curve course 32 represents the voltage
course when no ignition occurs. Curve course 33 shows the probe
voltage course when an ignition occurs in the relevant cylinder.
This comparison shows that here too, an evaluation of the ionic
current signal can be performed in the above described manner. The
use of ionic current measurement in the combustion chamber turns
out to be particularly favorable whenever the ionic current is
measured via the already existing electrodes of the spark plug in
the combustion chamber. This kind of ionic current measurement
process via the spark plugs is known in principle and has already
been proposed for the recognition of combustion misfires.
FIG. 10 shows the pressure course in a cylinder in comparison to
FIG. 9. In this connection, curve course 34 shows the course of the
combustion chamber pressure in a work cycle without ignition, while
curve course 35 represents the course of the combustion chamber
pressure with ignition.
The process is not only for use in reciprocating piston engines,
but in all engines with periodic fuel conversion, hence also in
rotating piston engines for example.
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